[ARM] realview: correct MMC clock rate

The MMC clock source is actually 24MHz, not 33MHz.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-realview/clock.c

@@ -104,7 +104,7 @@ static struct clk uart_clk = {
 
 static struct clk mmci_clk = {
 	.name	= "MCLK",
-	.rate	= 33000000,
+	.rate	= 24000000,
 };
 
 int clk_register(struct clk *clk)